An infrared detector of a quantum type is generally used at an extremely low temperature such as a liquid nitrogen temperature (77K). Therefore, the infrared detector packaged in a semiconductor package has to be cooled down by some method.
FIG. 3(a) is a sectional view showing a structure of a prior art infrared detector using a cooler head as a cooling means. In FIG. 3(a), an infrared detector 31 is packaged in a semiconductor package 32 which is 15 by 16 mm in dimensions and is formed of aluminum oxide (Al.sub.2 O.sub.3) or the like. The infrared detector 31 is electrically connected to the package 32 by wires 33. A lid 35 formed of a material such as ceramic which is 15 by 16 mm in dimensions, which is the same size as the package, and has a thickness of approximately 0.5 mm is bonded to the semiconductor package 32 via an adhesive agent 36. A cylindrical cooler head 34 having a diameter of 11 to 12 mm and formed of a material such as kovar which has the same thermal expansion coefficient as that of the lid 35 and also has high thermal conductivity is bonded to the surface of the lid using an adhesive agent 37. In addition, there is a space between the infrared detector 31 put in the semiconductor package 32 and the lid 35 and an air hole 35a is formed in the lid 35 (the air hole is omitted in the following drawings).
An almost cylindrical cooler head 34' whose upper part has the same square configuration as that of the lid 35 may be bonded as shown in FIG. 3(b).
In addition, in the infrared detector 31 a silicide film 312 of a metal such as Pt (PtSi) is disposed on a main surface of a silicon substrate 311 which is 12 by 16 mm in dimensions. On the surface of the film is disposed a silicon oxide layer 314 having a reflection film 313 of aluminum, and on the silicon oxide film layer 314 is disposed a protecting film 315 formed of a silicon nitride film. In addition, a pad 316, which is electrically in contact with the silicide film 312 for conducting a photoelectric current from the chip, is connected to the wire 33 outside the protecting film 315. Infrared light 317 incident on the back surface of the substrate 311 of the infrared detector 31 is photoelectrically converted on a Schottky surface of the silicide film 312 or is a once-reflected ray 318 incident on the reflection surface 313 and then photoelectrically converted on the Schottky surface of the silicide film 312. Then, the photoelectric current is transmitted to the wire 33 via the pad 316 and taken out of the chip.
In addition, it is necessary to cool down the infrared detector 31 in order to improve the photoelectric conversion characteristic on the Schottky surface during the above operation. This cooling is performed by cooling the package 32 through the lid 35 with the cooler head 34 as shown in FIGS. 3(a) and 3(b). As a method for cooling the cooler head 34 in this case, the cooler head 34 is brought into contact with liquid nitrogen or it is cooled using, for example a well-known SC cooler.
Next, a method for manufacturing the above semiconductor device package will be described. FIG. 4(a) is a view showing the semiconductor package 32 bonded to the lid 35 and FIG. 4(b) is an enlarged view showing a bonded part in FIG. 4(a) after fixing by heating (referred to as curing hereinafter). In FIG. 4(a), reference numeral 41 designates a guide fixture for aligning the semiconductor package 32 and the lid 35 at the time of bonding and reference numeral 42 designates an adhesive agent which is thinly spread between the semiconductor 32, the lid 35 and the guide fixture 41 through the curing after bonding.
At the time of bonding, the adhesive agent 36 is applied to the predetermined positions of the semiconductor package 32 and the lid 35. Then, the lid 35 is put on a concave part of the guide fixture 41, with the surface to which the adhesive agent 36 is applied upward. Then, as shown in FIG. 4(a), the semiconductor package 32 is put on the lid 35. The semiconductor package 32 is fixed to the lid 35 by curing the bonded parts, while a weight or the like is put on the semiconductor package 32. When the curing is completed, the bonding of the lid 35 is completed. Thereafter, the cooler head 34 is bonded to the lid 35 by applying the adhesive agent 37 on the surface of the lid 35 and patterning it into a desired configuration by using a template or the like.
Meanwhile, a part of the adhesive agent which was pressed out of the package 32 at the time of bonding is softened because its viscosity is once lowered by heat during the curing, whereby it is thinly spread into a space formed with the guide fixture 41 as shown in FIG. 4(b) and it is hardened on the surface of the lid 35. However, the guide fixture 41 is not bonded to the lid 35 by the projected adhesive agent 42 because Teflon or the like is applied to the contact surface between the guide fixture 41 and the lid 35.
If the adhesive agent 42 is on the lid 35 as described above, there can not be provided a desired pattern of the adhesive agent which is formed to bond the cooler head 34 by using the template. Even if the cooler head 34 is bonded by solder or the like instead of the adhesive agent, the solder can not be applied with high precision because of the projected adhesive agent 42. Particularly, its influence on a structure in which the cooler head is in contact with the whole surface of the lid as shown in FIG. 3(b). In either case, it is necessary to remove the projected adhesive agent using a scraper or the like. However, the surface of the lid 35 could be damaged when the adhesive agent is removed. When thermal stress is applied to this damaged part, a crack is generated in the lid 35, causing reliability of the apparatus to be decreased. In addition, the adhesive agent which could not be removed causes dust, whereby the reliability is also decreased.
In addition, in a case where the projected adhesive agent 42 does not reach the lid 35 and it is attached to a side of the lid 35, when modularization is implemented using a plurality of chips as shown in FIG. 5, a space d is present between the adjacent chips because of the adhesive agent on the side of the lid 35 and then alignment at the time of positioning can not be correctly performed.
As described above, according to the above-described prior art semiconductor device in which a lid is attached to a semiconductor package using an adhesive agent, the adhesive agent 42 is attached to the surface of the lid 35 or the like, which is an obstacle when the cooler head 34 is bonded on the surface of the lid 35, causing degradation of the reliability of the element.